C9orf72 FTD – Autosomal Dominant Inheritance — SCE Neurology MCQ

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ModerateNeurodegenerative DiseaseC9orf72 FTD – Autosomal Dominant InheritanceSCE Neurology

A 60-year-old man with FTD has a strong family history (mother and brother affected). Genetic testing reveals a C9orf72 hexanucleotide repeat expansion. His 30-year-old daughter asks about her risk. What inheritance pattern does C9orf72-related FTD follow?

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Correct answer: B — Autosomal dominant

C9orf72 hexanucleotide repeat expansion follows autosomal dominant inheritance with age-related penetrance. Each child of an affected individual has a 50% chance of inheriting the pathogenic expansion. Penetrance is incomplete and age-dependent — some carriers may not develop symptoms until late in life, and some may never develop clinical disease. Genetic counselling must be offered before any presymptomatic testing. A: It is dominant, not recessive. C: C9orf72 is on chromosome 9, not X-linked. D: Not mitochondrial. E: It can be familial with dominant inheritance.

Reference: EAN FTD Guidelines; C9orf72 Genetic Counselling Guidelines